Recently, with the growth of various printing technologies there is a growing trend in employing multicolor printing and using printing press with greatly improved printing speed. This tendency is also seen in newspaper printing. Multicolor printing of newsprint takes place under conventional printing conditions, i.e. penetration drying type inks are used for printing on conventional newsprint by high-speed coldset rotary presses to meet the need for immediate mass printing typical of newspaper printing and for cost-related reasons.
However, multicolor prints obtained under conventional newspaper printing conditions were very poor in color or sharpness as compared with conventional printing coated papers and as a result lacked visual appeal.
Therefore, newspaper pages requiring especially high final print quality such as color pages for multicolor advertising in newspapers or newspaper inserts are printed separately on coated printing papers or the like by conventional heatset rotary presses instead of high-speed coldset rotary presses. Under the present circumstances, the use of coldset rotary presses is stopped in newspaper publishing. This means that penetration drying type inks and high-speed coldset rotary presses as used in conventional newspaper printing are not practical to use with normal coated printing papers having a pigment coating layer on woodfree or wood-containing paper because the inks fail to dry when printing by coldset rotary presses, i.e., without using a post-dryer. However, printing effect is enhanced if printing were performed at low speed. Even if a pigment coating layer is provided on current newsprint, multicolor prints with good final quality cannot be obtained by applying penetration drying type inks when using high-speed coldset rotary presses because ink drying properties are very poor as in the case where a pigment coating layer is provided on normal uncoated paper.
A possible approach for improving print quality is to replace penetration drying type inks by heatset printing inks and switch from coldset rotary presses to heatset printers having dryer equipment for printing on newsprint. This approach has the disadvantages that equipment costs are high and printing costs thereby increase.
For these reasons, there have been strong demands for papers that satisfy the requirements of printability and beautiful multicolor prints using high-speed coldset rotary printing with penetration drying type newsprint inks.
For example, a newsprint having a coating layer containing a pigment having an oil absorbency of 65 cc/100 g or more was proposed (see patent document 1). However, the coating layer containing a pigment having high oil absorbency transfers much printing ink so that the amount of printing ink required increases, whereby ink drying is retarded and the problem of stickiness sometimes occurred in multicolor printing. A coated newsprint having high ink drying capability and ink density by defining dynamic wetting of the base paper and combining kaolin and a pigment having a defined average particle diameter was proposed (see patent document 2), but ink drying was retarded and the problem of stickiness sometimes occurred in multicolor printing. A slightly coated newsprint having 1.0 g/m2 or more and 4.0 g/m2 or less of a coating layer on a base paper and a moisture in paper of 4.5% or less was proposed (see patent document 3). However, color printed images were poor in tone reproduction and sharpness and insufficient in image quality or the like, and disadvantages such as stickiness occurred if the coat weight increased in multicolor printing.
Under these circumstances, there have been strong demands for coated papers for newsprint inks having high printability by eliminating stickiness without retarding ink drying and having good printability such as color reproduction and sharpness when printing using penetration drying type inks, especially when printing with high-speed coldset rotary presses using penetration drying type inks.
References:
Patent document 1: JPA HEI 1-174697.
Patent document 2: JPA HEI 4-57988.
Patent document 3: JPA 2003-286686.